Hindawi Publishing Corporation Neural Plasticity Volume 2016, Article ID 3898924, 8 pages http://dx.doi.org/10.1155/2016/3898924
Research Article Rostral Agranular Insular Cortex Lesion with Motor Cortex Stimulation Enhances Pain Modulation Effect on Neuropathic Pain Model Hyun Ho Jung,1 Jaewoo Shin,1,2 Jinhyung Kim,1 Seung-Hee Ahn,3 Sung Eun Lee,3 Chin Su Koh,1,4 Jae Sung Cho,1 Chanho Kong,1 Hyung-Cheul Shin,4 Sung June Kim,3 and Jin Woo Chang1,2 1
Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Republic of Korea Brain Korea 21 PLUS Project for Medical Science and Brain Research Institute, Yonsei University College of Medicine, Seoul, Republic of Korea 3 Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul, Republic of Korea 4 Department of Physiology, Hallym University College of Medicine, Chuncheon, Republic of Korea 2
Correspondence should be addressed to Jin Woo Chang;
[email protected] Received 17 June 2016; Revised 29 August 2016; Accepted 26 September 2016 Academic Editor: Long-Jun Wu Copyright Β© 2016 Hyun Ho Jung et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. It is well known that the insular cortex is involved in the processing of painful input. The aim of this study was to evaluate the pain modulation role of the insular cortex during motor cortex stimulation (MCS). After inducing neuropathic pain (NP) rat models by the spared nerve injury method, we made a lesion on the rostral agranular insular cortex (RAIC) unilaterally and compared behaviorally determined pain threshold and latency in 2 groups: Group A (NP + MCS; π = 7) and Group B (NP + RAIC lesion + MCS; π = 7). Also, we simultaneously recorded neuronal activity (NP; π = 9) in the thalamus of the ventral posterolateral nucleus and RAIC to evaluate electrophysiological changes from MCS. The pain threshold and tolerance latency increased in Group A with βMCS onβ and in Group B with or without βMCS on.β Moreover, its increase in Group B with βMCS onβ was more than that of Group B without MCS or of Group A, suggesting that MCS and RAIC lesioning are involved in pain modulation. Compared with the βMCS offβ condition, the βMCS onβ induced significant threshold changes in an electrophysiological study. Our data suggest that the RAIC has its own pain modulation effect, which is influenced by MCS.
1. Introduction Neuropathic pain is a neurodegenerative disease, caused by lesion or dysfunction of the central or peripheral nervous system. It is one of the most difficult types of pain to control because it is a multidimensional clinical entity mediated by many different pathophysiological mechanisms [1β4]. Drugrefractory neuropathic pain has been treated with invasive treatments such as lesioning or electrical stimulation therapy in the central or peripheral nervous system. Because of advantages such as reversibility and adjustability, neuromodulation therapy has become more popular. In 1991, Tsubokawa first reported the use of motor cortex stimulation (MCS) in a patient with chronic, drug-resistant
neuropathic pain [5]. MCS was initially applied to central pain secondary to thalamic stroke, but, over time, its usage expanded to various other types of neuropathic pain. The clinical literature reveals that chronic MCS shows approximate 45 to 75% of pain control rate [6β10]. Thus, the MCS procedure was accepted as a promising therapy for patients with severe drug-refractory pain. However, despite the clinical use of MCS for pain modulation, the mechanisms underlying its effects remain unclear. There were several imaging studies and electrophysiological investigations performed to solve the mechanism of MCS, and they showed that many brain structures are activated after MCS [11β13]. MCS was found to attenuate hyperactivity
2 of thalamic neurons [5]. We have previously reported that MCS modulate pain-signaling pathways and suppress activation of the ventral posterolateral nucleus (VPL) [14]. The insular cortex, although not yet extensively explored, also showed clear involvement in pain perception through imaging studies using PET or fMRI. Within the insular cortex, in animal studies, the rostral anterior insular cortex (RAIC) has extensive reciprocal corticocortical connections which shows its involvement in multiple aspects of pain behavior [15]. Also after making a lesion in the RAIC, there were diminished pain-related behaviors in neuropathic models without lateralization, which shows clear evidence of the pain modulation role of RAIC [16]. The aim of this study was to evaluate the role of pain modulation in the RAIC during MCS.
2. Materials and Methods 2.1. Animals. All procedures were conducted according to the guidelines of the Ethical Committee of the International Association for the Study of Pain and approved by the Institution Animal Care and Use Committee (IACUC) of Yonsei University [17]. Male Sprague-Dawley rats (π = 23) weighing 180β200 g were used in this study. Three animals were housed per laboratory cage with food and water available ad libitum. Light was controlled under a 12 h light/dark (light on between 07:00 am and 19:00 pm) cycle. The temperature was maintained at 22 Β± 2β C and relative humidity was at 55 Β± 5%. Animals were allowed to acclimate for at least a week before surgery and behavioral testing. The behavior-based study of the MCS effect was observed in two animal groups: Group A, a neuropathic pain group (π = 7), and Group B, neuropathic pain + RAIC lesion group (π = 7). Furthermore, neuronal activity of MCS effect was measured electrophysiologically in the neuropathic pain group (π = 9). 2.2. Surgical Procedures 2.2.1. Surgical Procedures for Pain Model. To induce neuropathic pain, we used the spared nerve injury (SNI) method [18]. Rats were deeply anesthetized with pentobarbital sodium (50 mg/kg, intraperitoneally), and the left sciatic nerve was exposed. Under a surgical microscope (Olympus, Tokyo, Japan), the three major divisions of the sciatic nerve were exposed, and the common peroneal and tibial nerves were completely ligated and transected. Hemostasis was completed, and the cut was closed with muscle and skin sutures. 2.2.2. MCS Electrode Implant. For MCS, we used a custommade liquid crystal polymer electrode [19]. One week after establishing the animal model for neuropathic pain, we measured the pain threshold to determine whether the neuropathic pain had been effectively induced. A detailed description of our behavior test for measuring pain threshold is in Section 2.3.1. After the behavior test, rats that did not exhibit a neuropathic pain response were excluded from this study. To implant the MCS electrode, rats were anesthetized with pentobarbital sodium (50 mg/Kg, intraperitoneally) and fixed
Neural Plasticity with a stereotaxic frame (Narishige, Tokyo, Japan). The scalp was opened and the skull was exposed. To place the electrode on the left hindlimb area of the primary motor cortex [20], we made a rectangular hole (2.0 mm Γ 2.0 mm). The coordination was from β0.2 to +1.8 mm from the Bregma and from 0.5 to 2.5 mm from the midline. The electrode was placed in the epidural space, and the electrode was firmly fixed using bolts and glue. The scalp was secured with sutures after completing all procedures. 2.2.3. RAIC Lesion. In Group B, prior to implanting the MCS electrode, we made a burr hole that allowed us to insert an electrode in the target site (RAIC, AP: anteroposterior direction: +1.0 mm from the Bregma, ML: midline: +4.5 mm right side, lateral from midline, and DV: dorsoventral direction: β6.0 mm from the dura mater) [16]. After inserting electrodes in the target coordinates, we delivered an electrical pulse of 0.1 mA for 10 seconds for the RAIC lesioning. Then, the lesioning electrode was removed and the MCS electrode was implanted. 2.3. Behavior Tests. The time table for SNI modeling and behavioral test in the two groups is presented in Figure 1. 2.3.1. Measuring Tactile Threshold. Rats were placed inside acrylic cages (8 Γ 10 Γ 20 cm) on a wire mesh grid for measuring the mechanical threshold. After 30 minutes of adaptation, a series of von Frey filaments (0.4, 0.6, 1, 2, 4, 6, 8, and 15 g of bending force) were applied to the lateral edge of the left hind paw. We calculated the tactile threshold by using the up and down method [21]. 2.3.2. Measuring Response Latency. To measure the response latency, rats were placed in the same acrylic cages. After 30 minutes of adaptation, we applied painful stimulation to the left hindlimb, using a Plantar test unit (model 37370, Ugo Basile Biological Instruments, Comerio, VA, Italy) which measures the time by gradual application of strength automatically. When the rat initiated a withdrawal response, the Plantar test unit recorded the duration of resistance from stimulation and the value of final force. We measured the latency three times and used the average value for analysis. 2.3.3. Behavioral Test Schedule and MCS Parameters. After 30 min of adaptation in the acryl cages, MCS was turned on (biphasic pulses of 65 Hz, 210 πs, 80 πA, for 30 min) using a stimulator (Model 2100, A-M Systems, Sequim, WA, USA). Behavioral tests were conducted at the following time points: before stimulation, 30 minutes after the start of stimulation, immediately after ceasing stimulation, and 5 times every 10 min. 2.4. Electrophysiology. We simultaneously recorded neuronal activity in the VPL of the thalamus and RAIC of NP model to compare the changes before and after MCS. Rats (π = 9), confirmed NP models after behavioral tests, were anesthetized with urethane (1.3 g/kg), and a microelectrode (573220, A-M Systems, Sequim, WA, USA) was inserted into the VPL and RAIC to obtain extracellular recordings of single unit activity.
Neural Plasticity
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Pre-test & SNI modeling
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SNI model verification & MCS implant with/ without lesion
Behavior test
Behavior test
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SNI
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Figure 1: The timetable of spared nerve injury (SNI) modeling and behavioral test in two groups (Group A: neuropathic pain + motor cortex stimulation and Group B: neuropathic pain + rostral agranular insular cortex lesion + motor cortex stimulation).
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DCI VCI
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3 2 Pir 1 Io Bregma 1.08 mm
Figure 2: Histological verification of rostral agranular insular cortex (RAIC) lesions with fusing Mai atlas. Data from red dots (π = 7) were analyzed in this study. Blue dots were excluded from data analysis.
Two-channel array electrodes were positioned stereotactically in the VPL (ML: +2.8 mm; AP: β2.2 mm; DV: β6.0 mm from the Bregma) and the RAIC (AP: +1.0 mm; ML: +4.5 mm; DV: β6.0 mm from the Bregma). The neuronal activities were recorded for 5 minutes. During acquisition of the neural signal, mechanical stimulation, using 300 g of von Frey hair filaments, was applied to the ratsβ left hind paw area. Signals from the microelectrode were amplified (amplifier model 1700, AM Systems, Sequim, WA, USA), and the signal was converted and transmitted to the recording system using an AD converter (Micro 1401, Cambridge Electronic Design Limited, Milton Road, Cambridge, UK). The data were stored by Spike 2 (Cambridge Electronic Design Limited, Milton Road, Cambridge, UK). Recorded waveforms were analyzed using Offline Sorter (Plexon Inc., USA), NeuroExplorer (NeuroExplorer Inc., USA).
Signal analysis was obtained for 20 sec before and after MCS. Because of firing differences in each region following MCS, the interval between the signal analyses was regulated. 2.5. Histological Verification of RAIC Lesion. To verify the RAIC lesioning after completion of our experiments, rats were intracardially perfused with normal saline and fixed with 4% paraformaldehyde in PBS (pH = 7.4). The brain was carefully removed and prepared for frozen sectioning. Coronal sections of 30 πm thickness were obtained using a microtome with deep freezer (Figure 2). The slices were dyed using cresyl violet. Microscopy images were obtained using a microscope (Olympus, Tokyo, Japan). 2.6. Statistical Analysis. Data are reported as mean Β± SEM. Behavioral test data were analyzed using one-way and
Neural Plasticity Mechanical thresholds (g)
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Table 1: Mechanical threshold measurement comparisons for Groups A and B at various time points: before (Pre), during (15 and 30 minutes), and after (40, 50, 60, and 70 minutes) motor cortex stimulation. Motor cortex stimulation began at 15 min time point.
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βββ
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Mechanical thresholds (gram) Group A Group B 0.470 Β± 0.090 2.750 Β± 0.456 10.080 Β± 1.951ββ 3.859 Β± 0.698βββ 2.940 Β± 0.423βββ 8.596 Β± 2.454β βββ 2.226 Β± 0.321 8.428 Β± 2.478β 1.709 Β± 0.360 5.015 Β± 1.204 1.010 Β± 0.339 3.646 Β± 0.839 0.858 Β± 0.218 3.045 Β± 0.741
Time (minute)
(Week) Group A Group B
Figure 3: The change of mechanical thresholds was measured every week after pain modeling. Group B showed higher mechanical thresholds compared to Group A at 3rd and 4th weeks, which was statistically significant [two-way analysis of variance (ANOVA) with Bonferroni post hoc tests; βββ π < .0001].
Pre 15 30 40 50 60 70
Comparisons among groups were made using repeated measures one-way analysis of variance (ANOVA). βββ π < .001, ββ π < .01, and β π < .05 for comparisons.
two-way analysis of variance (ANOVA) with Bonferroniβs post hoc test. Electrophysiological data were evaluated using the Friedman test followed by Dunnβs post hoc test. The π values of
